1. Field of the Invention
The present invention relates to a zoom lens for a digital camera, a video camera or a compact camera.
2. Description of the Related Art
In general, in a zoom lens, the focal length can be continuously varied by moving movable variable power lens groups (a plurality of lens groups which move along the optical axis upon zooming) in a stepless fashion. In a single lens reflex camera in which an object image formed by a photographing lens system is viewed through a view finder, it is preferable to be able to stop the variable power lens groups at a desired position. In a single lens reflex camera in which the focal length of the photographing lens is detected electrically and is used to control predetermined operations, it is possible to mechanically stop the variable power lens groups at a desired focal length position so as to prevent the object image from appearing unnatural due to the discontinuous zooming operation. Furthermore, the focal lengths can be detected stepwise at practical intervals, and can be used to control a predetermined operation. Namely, the function of stopping the variable power lens groups itself at a desired position is a different matter not to be confused with the stepwise detection of the focal length.
In a digital camera, video camera or compact camera, in which an image other than an image formed by a photographing optical system is viewed through a finder optical system, the stepless stoppage of the variable power lens groups in the finder optical system has less merit. Therefore, the variable power lens groups are stopped stepwise and the focal length is detected stepwise.